Until advances in clutch design made by the assignee of the subject invention, clutch rollers were generally retained to the clutch cage by the roller energizing springs, which loaded the rollers against rest surfaces on the cage. This system had the advantage of simplicity, since it required no extra clutch components or significant structural modifications. However, the security or strength of the roller retention was only as strong as the spring, and the springs cannot be made very strong without increasing roller spin. Consequently, the clutches had to be handled very carefully to prevent the rollers from dislodging.
Some designs proposed to retain the rollers with projections stamped out of the clutch cage side rails, which fitted into hollowed out ends of the rollers, and so retained the rollers to the cage permanently. Sometimes the projections themselves were also intended to serve as the roller energizing springs. While the roller retention so provided would be secure, the possible roller travel during clutch operation would be inherently limited to less than the diameter of the roller. This is too severe a limitation to be practical except in the most limited applications.
Two newer roller clutches proposed by the assignee of the subject invention give a very secure roller retention that does not limit roller travel during clutch operation. These designs take advantage of the way in which many roller clutches are installed, called the "ringing in" method. The clutch is first installed to the cam race, which locates the outer surfaces of the rollers slightly beyond the circle where the cylindrical pathway surface of the pathway race is ultimately located. When the pathway race is installed, it is pushed axially over the rollers and twisted a partial turn at the same time. This twisting action shifts the rollers down the ramps of the cam race, and compresses the springs. In one, disclosed in U.S. Pat. No. 4,724,940, a specially designed spring latches to the cage to hold the roller in a secure shipping position which, while it is not totally independent of the spring, is totally independent of the resilience of the spring. When the pathway race is rung in, the rollers disengage the spring latches, after which the rollers and springs are totally freed from the cage.
In another recent design, an entirely new type of component is added to the clutch. A series of roller control cars, one for each roller, holds each roller individually. The cars slide back and forth between the cage side rails with the rollers during clutch operation, so roller travel is not limited. During shipping, the car is latched to the cage similar to the way in which the specially designed spring referred to above is latched to the cage. The ringing in operation releases the latch to free the car from the cage. The rollers and springs may be totally conventional, but there is, of course, the added expense of the new components. There may be applications where, because of cost and space limitations, a clutch design that had equally secure roller shipping retention, but which used conventional springs and which required no new components would be useful.